Very little is known about the physiology of sucrose transport into developing rice grains. While the post-phloem unloading sucrose transport pathway has been described in detail, quantitative studies of sucrose uptake including the role of membrane transport are lacking. This has limited our understanding of carbon partitioning and the control of rice yield. We are interested in studying the sucrose-proton cotransport system that has been reported as being expressed in rice endosperm. Based on previous reports that the aleurone layer is symplastically isolated from the phloem, we chose to investigate sucrose-proton cotransport in rice aleurone cells. Aleurone protoplasts were isolated from Oryza sativa aleurone peels using standard cell wall degradation enzymes. Very high osmolarity, 0.8-1 M mannitol or sorbitol, was essential for obtaining high yields of 5,000-30,000 viable protoplasts/10 grains. Protoplasts were 20-40 mm in diameter and had granular cytoplasm. These traits were consistent with previous reports on rice aleurone layer morphology and were confirmed after our study of grain anatomy using light microscopy. The aleurone protoplasts proved to be a system amenable to whole cell patch clamping. We formed high resistance seals (3 Giga-ohms) without difficulty and assessed whole cell currents from protoplasts bathed in solutions containing different levels of K+. The whole cell conductance of these cells was dominated by an instantaneous outward current as well as a slow developing, time dependent inward current. Future experiments, designed for modeling rice yield, include testing the suitability of this aleurone whole cell system for quantitative studies of sucrose-proton cotransport.

Key words: aleurone, carbon partitioning, modeling, patch clamping, rice, sucrose transport